1. Field of the Invention
This invention relates to the removal of dust from air. More specifically, dust is removed from air by means of an electrostatic precipitator apparatus.
2. Description of the Prior Art
Prior single-stage and two-stage electrostatic dust collectors operate on well established principles wherein dust is passed through an ionized region, a corona, and thereby charged and then collected due to forces applied to the charged particles by the corona field and any other static electric fields through which the particles are passed. In most precipitators dust deposits on rigid surfaces such as collection plates or casing walls as a dry cake and is subsequently removed by periodic rapping to cause the cake to drop into collection bins. The collected cake can reduce corona current, cause arcing, or cause a reverse current discharge from the dust, called back corona. These phenomena reduce collection efficiency. Additional efficiency loss occurs when dry dust is reentrained into the flowing gas during rapping. Finally, dry dust of a combustible nature, such as cotton dust, is a fire hazard when accumulated in an area where electrical arcing occurs.
To combat some problems of dry electrostatic precipitation wet electrode systems have been developed in several forms. The operation principle is the same as that for single- and two-stage precipitators with dry collection except that additional devices are provided to wet or rinse the dust collection surfaces and thereby eliminate removal by rapping. Such wetting devices may be continuous or intermittent liquid spray jets near collection surfaces, mechanically traversing liquid jet cleaners, or flow ports to provide a film coating over the dust collection surface. These devices add complexity to electrostatic precipitators and often inadequately wet collection surfaces thereby allowing dust or dust residues to accumulate in the precipitator. The maintenance of a continuous flowing uniform liquid film over all collection surfaces is essentially unattainable under field conditions with existing surface wetting and rinsing devices. The inadequacy of present wet-wall precipitators is evidenced by their limited share of the present commercial market as compared to dry precipitators with rappers.